During fabrication of semiconductor devices, various surfaces are formed. Many of such surfaces do not have uniform height, and therefore, the wafer thickness is also non-uniform. Further, surfaces may have defects such as crystal lattice damage, scratches, roughness, or embedded particles of dirt or dust. For various fabrication processes to be performed, such as lithography and etching, height non-uniformities and defects at the surface of the wafer must be reduced or eliminated. Various planarization techniques are available to provide such reduction and/or elimination. One such planarization technique includes mechanical and/or chemical-mechanical polishing (abbreviated herein as “CMP”).
The process of planarization is used to remove material, and preferably achieve a planar surface, over the entire chip and wafer, sometimes referred to as “global planarity.” Conventionally, the process of planarization, and particularly CMP, involves the use of a wafer carrier that holds a wafer, a polishing pad, and an abrasive slurry that includes a dispersion of a plurality of abrasive particles in a liquid. The abrasive slurry is applied so that it contacts the interface of the wafer and the polishing pad. A table or platen has a polishing pad thereon. The polishing pad is applied to the wafer at a certain pressure to perform the planarization. At least one of the wafer and a polishing pad are set in motion relative to the other. In some planarization processes, the wafer carrier may or may not rotate, the table or platen may or may not rotate and/or the platen may be moved in a linear motion as opposed to rotating. There are numerous types of planarization units available which perform the process in different manners.
The use of abrasive slurries in wafer fabrication has proven problematic for several reasons. First, abrasive slurries that contain a plurality of abrasive particles in a dispersion tend to be unstable. In particular, not only do the abrasive particles settle, the abrasive particles also tend to agglomerate, both phenomenon resulting in a nonuniform slurry composition. This, in turn, creates wide variability in the polishing results. Second, it is known within the art that the composition of the slurry tends to be very specific with the desired planarization process, i.e., one slurry may not be suitable for a variety of processes.
Also, conventional polishing pads pose planarization difficulties. Such pads may glaze, or become embedded with debris, during planarizing. This requires the pads to be conditioned such that the pads can be reused. Conditioning typically involves removal of the debris from the polishing pad using mechanical means with or without application of a solution. Conditioned pads typically lead to subsequent unpredictable planarization results because of the unpredictability in removal of debris from the pad itself during conditioning.
Fixed abrasive articles used in place of conventional polishing pads are also known and used in planarization processes. Such fixed abrasive articles include a plurality of abrasive particles dispersed within a binder adhered to at least one surface of a backing material. For certain situations, fixed abrasive articles are advantageous; however, conventional abrasive slurries are typically incompatible with fixed abrasive articles for many planarization processes.
The planarization of a surface that includes platinum and other Group VIII metals typically involves more mechanical than chemical action during a polishing process because they are relatively chemically inert and/or have relatively few volatile produces. Such mechanical polishing uses alumina and silica particles. Unfortunately, mechanical polishing tends to cause the formation of defects (e.g., scratches and particles), both of which can be detected optically, rather than the clean removal of the platinum.
Thus, there is still a need for methods for planarizing an exposed surface of a substrate that includes platinum and other Group VIII metals, particularly in the fabrication of semiconductor devices.